How to Update a WinForms ProgressBar During Asynchronous Calculations?

WinForms Asynchronous Calculation Progress Bar Usage Guide

When using external libraries that perform lengthy calculations, it is useful to display a progress bar to provide feedback to the user. In WinForms, you can use the ProgressBar control for this purpose.

Use of progress bar in synchronous calculation

If the calculations are performed synchronously in your Form class, simply use the PerformStep() method to increment the ProgressBar after each calculation completes. For example:

private void button1_Click(object sender, EventArgs e)
{
    progressBar1.Maximum = 100000;
    progressBar1.Step = 1;

    for(int j = 0; j < 100000; j++)
    {
        // Perform calculation
        progressBar1.PerformStep();
    }
}

Use of progress bar in asynchronous calculation

However, if the calculation is performed asynchronously in an external method, the ProgressBar cannot be updated directly from that method. Instead, use the BackgroundWorker class to perform calculations and report progress back to the UI thread.

Use BackgroundWorker

The BackgroundWorker class allows you to perform time-consuming operations in a separate thread while providing progress updates to the main UI thread. It has a ReportProgress method that allows you to send the progress percentage back to the UI thread.

The following is an example using BackgroundWorker:

private void button1_Click(object sender, EventArgs e)
{
    progressBar1.Maximum = 100;
    progressBar1.Step = 1;
    progressBar1.Value = 0;
    backgroundWorker.RunWorkerAsync();
}

private void backgroundWorker_DoWork(object sender, DoWorkEventArgs e)
{
    var backgroundWorker = sender as BackgroundWorker;
    for (int j = 0; j < 100; j++)
    {
        // Perform calculation
        backgroundWorker.ReportProgress(j);
        Thread.Sleep(100); // 模拟耗时操作
    }
}

private void backgroundWorker_ProgressChanged(object sender, ProgressChangedEventArgs e)
{
    progressBar1.Value = e.ProgressPercentage;
}

In this example, the calculation is performed in the backgroundWorker_DoWork method, while the backgroundWorker_ProgressChanged method is used to update the ProgressBar on the UI thread.

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